I'm trying to get the achievement for collection of all weapons and items in SCIV.
However, I'm not exactly sure how the item unlocking works.

I know about the treasure chests in the tower, and how to get them and what-not.

What I'm unsure of is how to get other items.
For example when I started, I just played a few games and randomly I had new items, there where no prompts of any sort explaining when I obtained them, I just saw them as new in the Character Creation. Some items I later found out are supposed to be obtained in the tower, such as the minotaur head, however I never played that level in the tower and somehow unlocked the minotaur head.

So how do you unlock new items other than the Tower and beating story? Is it time based, such as every hour of play you get a new item? Or is it win based, after 100 wins you get a new item?